Document Type : Original Article
Abstract
Concrete is the most common material used to line irrigation canals and must maintain its durability for the lifetime of the canal. Compressive strength has been used as an index to control the quality of concrete; concrete that remains durable under freeze-thaw conditions is that with high compressive strength. Research has shown that concrete linings can show suitable compressive strength in the first days of existence, but begin to decompose after a period and lose the property of durability. The present study examined the relationship between compressive strength and the durability parameters of initial water absorption, final water absorption, water penetration depth and porosity in the Variyaneh and Dingel-e Kahriz irrigation canals in the province of Hamedan. Laboratory testing was carried out on 27 cores (69 mm in diameter; different lengths) extracted from the concrete linings of canals. The cores were prepared and their compressive strength and durability parameters were determined. The results show an inverse linear relationship between the compressive strength and density of the samples and their porosity. The durability parameters of initial water absorption, final water absorption, and water penetration depth showed no significant relationship. The results indicate that compressive strength is not sufficient for evaluation of the durability of concrete lining. Of the 27 cores, 40% had acceptable compressive strength. Of these, 50% showed acceptable durability parameters for exposure to freeze-thaw. The results also showed that the mean penetration depth and porosity of the samples were >2.5 times greater than the maximum recommended values and that the initial and total water absorption values were >1.5 times greater than the maximum recommended values. It is evident that the concrete linings will decompose more quickly than the anticipated lifetime from the influence of water and other expansive solute solutions in cold weather. It was noted that samples having similar compressive strengths had durability parameters that were greater or less than acceptable values. These results suggest that the compressive strength of concrete alone is insufficient to ensure durability and it is necessary to examine additional parameters affecting the lifetime of the concrete linings.
Keywords
C 642. Annual Book of ASTM Standards. Philadelphia.
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